Re: [Xen-devel] [PATCH] xen/blkback: Squash the discard support for 'file' and 'phy' type.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Mar 14, 2012 at 09:48:21AM +0000, Jan Beulich wrote:
> >>> On 13.03.12 at 23:52, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> >>> wrote:
> > The only reason for the distinction was for the special case of
> > 'file' (which is assumed to be loopback device), was to reach inside
> > the loopback device, find the underlaying file, and call fallocate on it.
> > Fortunately "xen-blkback: convert hole punching to discard request on
> > loop devices" removes that use-case and we now based the discard
> > support based on blk_queue_discard(q) and extract all appropriate
> > parameters from the 'struct request_queue'.
> > 
> > CC: Li Dongyang <lidongyang@xxxxxxxxxx>
> > CC: Jan Beulich <JBeulich@xxxxxxxx>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> (with a few minor remarks below)
> 
> > --- a/drivers/block/xen-blkback/blkback.c
> > +++ b/drivers/block/xen-blkback/blkback.c
> > @@ -419,21 +419,17 @@ static int dispatch_discard_io(struct xen_blkif 
> > *blkif,
> >     int err = 0;
> >     int status = BLKIF_RSP_OKAY;
> >     struct block_device *bdev = blkif->vbd.bdev;
> > -
> > +   unsigned long secure = 0;
> 
> Mind keeping the blank line and dropping the pointless initializer (which
> future gcc is likely going to be warning about)?

<nods>
> 
> >     blkif->st_ds_req++;
> >  
> >     xen_blkif_get(blkif);
> > -   if (blkif->blk_backend_type == BLKIF_BACKEND_PHY ||
> > -       blkif->blk_backend_type == BLKIF_BACKEND_FILE) {
> > -           unsigned long secure = (blkif->vbd.discard_secure &&
> > -                   (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
> > -                   BLKDEV_DISCARD_SECURE : 0;
> > -           err = blkdev_issue_discard(bdev,
> > -                           req->u.discard.sector_number,
> > -                           req->u.discard.nr_sectors,
> > -                           GFP_KERNEL, secure);
> > -   } else
> > -           err = -EOPNOTSUPP;
> > +   secure = (blkif->vbd.discard_secure &&
> > +            (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
> > +            BLKDEV_DISCARD_SECURE : 0;
> > +
> > +   err = blkdev_issue_discard(bdev, req->u.discard.sector_number,
> > +                              req->u.discard.nr_sectors,
> > +                              GFP_KERNEL, secure);
> >  
> >     if (err == -EOPNOTSUPP) {
> >             pr_debug(DRV_PFX "discard op failed, not supported\n");
> > --- a/drivers/block/xen-blkback/xenbus.c
> > +++ b/drivers/block/xen-blkback/xenbus.c
> > @@ -393,52 +393,37 @@ int xen_blkbk_discard(struct xenbus_transaction xbt, 
> > struct backend_info *be)
> >     char *type;
> >     int err;
> >     int state = 0;
> > +   struct block_device *bdev = be->blkif->vbd.bdev;
> > +   struct request_queue *q = bdev_get_queue(bdev);
> >  
> > -   type = xenbus_read(XBT_NIL, dev->nodename, "type", NULL);
> > -   if (!IS_ERR(type)) {
> > -           if (strncmp(type, "file", 4) == 0) {
> > -                   state = 1;
> > -                   blkif->blk_backend_type = BLKIF_BACKEND_FILE;
> > +   if (blk_queue_discard(q)) {
> > +           err = xenbus_printf(xbt, dev->nodename,
> > +                   "discard-granularity", "%u",
> > +                   q->limits.discard_granularity);
> > +           if (err) {
> > +                   xenbus_dev_fatal(dev, err,
> > +                           "writing discard-granularity");
> > +                   goto kfree;
> 
> Unrelated to the patch here, but failure to write any sort of extension
> data shouldn't be considered fatal - the backend can well work without
> these, and it should be left to the frontend to decide whether it wants
> to live without the unavailable extensions.

<nods>. Let me whip up another patch that removes these 'fatal' cases
and is based on this one.

> 
> Jan
> 
> > +           }
> > +           err = xenbus_printf(xbt, dev->nodename,
> > +                   "discard-alignment", "%u",
> > +                   q->limits.discard_alignment);
> > +           if (err) {
> > +                   xenbus_dev_fatal(dev, err,
> > +                           "writing discard-alignment");
> > +                   goto kfree;
> >             }
> > -           if (strncmp(type, "phy", 3) == 0) {
> > -                   struct block_device *bdev = be->blkif->vbd.bdev;
> > -                   struct request_queue *q = bdev_get_queue(bdev);
> > -                   if (blk_queue_discard(q)) {
> > -                           err = xenbus_printf(xbt, dev->nodename,
> > -                                   "discard-granularity", "%u",
> > -                                   q->limits.discard_granularity);
> > -                           if (err) {
> > -                                   xenbus_dev_fatal(dev, err,
> > -                                           "writing discard-granularity");
> > -                                   goto kfree;
> > -                           }
> > -                           err = xenbus_printf(xbt, dev->nodename,
> > -                                   "discard-alignment", "%u",
> > -                                   q->limits.discard_alignment);
> > -                           if (err) {
> > -                                   xenbus_dev_fatal(dev, err,
> > -                                           "writing discard-alignment");
> > -                                   goto kfree;
> > -                           }
> > -                           state = 1;
> > -                           blkif->blk_backend_type = BLKIF_BACKEND_PHY;
> > -                   }
> > -                   /* Optional. */
> > -                   err = xenbus_printf(xbt, dev->nodename,
> > -                           "discard-secure", "%d",
> > -                           blkif->vbd.discard_secure);
> > -                   if (err) {
> > -                           xenbus_dev_fatal(dev, err,
> > +           state = 1;
> > +           /* Optional. */
> > +           err = xenbus_printf(xbt, dev->nodename,
> > +                               "discard-secure", "%d",
> > +                               blkif->vbd.discard_secure);
> > +           if (err) {
> > +                   xenbus_dev_fatal(dev, err,
> >                                     "writting discard-secure");
> > -                           goto kfree;
> > -                   }
> > +                   goto kfree;
> >             }
> > -   } else {
> > -           err = PTR_ERR(type);
> > -           xenbus_dev_fatal(dev, err, "reading type");
> > -           goto out;
> >     }
> > -
> >     err = xenbus_printf(xbt, dev->nodename, "feature-discard",
> >                         "%d", state);
> >     if (err)
> 

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